recycling opportunities in the uk for aluminium-bodied motor cars

ELSEVIER Resources, Conservation and Recycling 15 (1995) 181-191

r e s o u l ~ c e s j

conservation and recycling

Recycling opportunities in the UK for aluminium- bodied motor cars

Graeme Hoyle Advanced Technology Centre, University of Warwick, Coventry, CV4 7AL, England, UK

Received 5 January 1995; accepted 28 March 1995

Abstract

The purpose of this paper is to review, and draw attention to, issues raised by the recycling of wrought aluminium from motor cars, even though the time horizon for significant arisings of such aluminium scrap is in the order of 20 years from now. Recycling of specific grades of wrought aluminium will be viable only when a means of positively identifying different types of scrap is available. A solution must be reliable, rapid, and low-cost; probably used in conjunction with a vehicle shredder. Such a system of identification will eliminate the need for costly hand-dismantling and segregation. Simple segregation of cast and wrought alloy will, however, be essential when wrought aluminium from car bodies dominates the scrap arisings. Such segregation will produce two high- value scrap products. The first of which will be similar to the A380 casting alloy specification, maintaining the current supply of this scrap, and the second will be a composite of wrought alloys. These issues are relevant to the aluminium scrap industry, which will have to accommodate future changes in the composition of the scrap it receives, and the motor industry, which may adopt in-house recycling of wrought alloy in order to offset the high purchase cost of aluminium.

Keywords: Aluminium recycling; Automobile recycling; Aluminium automobile

I. Introduction

Aluminium, in a variety of forms, has been used for the manufacture of cars since the

earliest days of the motor industry. But with a few exceptions, the LandRover being the most successful in this respect, it has not toppled steel from its position as the industry's favourite metal; until now.

A new generation of cars, constructed largely of aluminium instead of steel, is appearing on our roads. The Audi A8 executive saloon is only the first, and it has attracted a waiting list of 3 months only days after its launch. Among the benefits promised by cars containing substantial quantities of aluminium are these: they will consume less energy; create fewer

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182 G. Hoyle /Resources, Conservation and Recycling 15 (1995) 181-191

polluting emissions; be rust resistant; and they will equal or better the all-round performance of today's cars.

However, the use of large amounts of wrought and cast aluminium in motor cars raises questions about the practical issues involved if the aluminium industry is to make the most of the opportunity to recycle it.

2. The aluminium industry

Fuelled by the post-war boom in transportation, consumer goods, and packaging, the primary and secondary aluminium companies enjoyed rapid growth until the energy crisis of the 1960s and 1970s [ 1 ]. Up until then, primary producers had largely ignored secondary production, preferring to leave it to local metal merchants and remelters. But high energy costs soon squeezed their profit margins, forcing them to enter secondary production as a way of cutting costs. Recycling of aluminium takes only 5% of the energy required for primary production.

Nowadays, additional costs of production: labour, transport, and environmental compli- ance, are persuading aluminium companies to relocate their primary smelters in developing countries where costs are lower and supplies of bauxite are situated nearby. Facilities remaining in developed countries are mainly for secondary aluminium, and these compete with the established secondary sector [ 2,3 ].

Furthermore, the recent collapse of the former Soviet empire has threatened to de-stabilise world trade in aluminium [4]. Eager for hard currency, and lacking their traditional defence markets to sell to, countries in Eastern Europe sold substantial quantities (about 10% of world production) of aluminium ingot into the world market in 1992-3, causing a collapse in prices and a massive stockpile of metal to accumulate. International intervention has stabilised the situation but not without plant closures around the world and the introduction of quotas.

Despite these recent difficulties the UK still produces both primary and secondary aluminium, and has done so for many years. Fig. 1 illustrates the main flows of aluminium

castings J~ forgings Ravt ~ ~ extrusion materials

smelter J I I '7 ) Users

U" II j'- /pr°cessScrap /q I L l .o,,o.

' / I / I remelts I

~ l smolto r i ! ~ Castinos

I I Fragmentisor and ~ Old alloy separation Scrap

Fig. I. The UK aluminium industry - Automobile manufacture and recycling.

G. Hoyle / Resources, Conservation and Recycling 15 (1995) 181-191 183

with respect to automotive manufacture and recycling. Aluminium packaging: foil, and beverage cans, has a largely separate infrastructure [5,6].

Primary aluminium enters the system at the top left of the figure. In 1993 about 581 000 tonnes of primary ingot was imported in to the UK, and a further 239 000 tonnes was smelted from ore. The ingot is subsequently converted into semi-manufactured products for the auto industry. These include forgings, sheet, extrusions, sections, and bars.

For the reasons stated, secondary production is a rapidly growing sector of the aluminium business. Much of this expansion is in remelting of in-process scrap generated by semi- manufacturers. The majority of this is remelted in-house, as a single-grade alloy, and reused. The remainder is sent to an independent remelter. This practice is called tolling, and in 1993 independent remelters tolled about 417 000 tonnes of process scrap; an amount nearly as large as primary production and imports. As well as converting their customers scrap, remelters buy scrap for their own use if it is high quality and of a guaranteed grade. They use it instead of virgin ingot, or alloying elements, to bring their customers aluminium up to the required standard.

A further 237 000 tonnes of secondary aluminium is produced each year exclusively from old scrap. Old scrap includes car scrap and scrap from unknown sources. It is bought by primary and secondary smelters who will use it to produce casting grade alloy. Metal merchants sort the better quality aluminium from the scrap they collect and sell it directly to secondary smelters. The remaining poor quality aluminium and aluminium-iron mixture is fragmentised and sorted automatically in a heavy-media plant [ 7 ]. The resulting product, although it comes from a variety of sources, is worth about 60% of the LME 1 ingot price because the quality is guaranteed. About 65 000 tonnes of fragmentised aluminium scrap arises from end-of-life cars each year.

2.1. Car scrapping and conversion in the UK

Car dismantlers and scrap dealers collect about 1 300 000 cars a year from insurance companies, the local authorities, and the general public. They strip out all the high value metals, including aluminium, and remove all the saleable parts, for example: batteries, engines, windows, and bumpers. What is left, the hulk, is bought by metal merchants who will convert it into high-grade steel scrap, and salvage the remaining non-ferrous metals.

Conversion begins by flattening the hulk and feeding it, along with a mixture of commercial light-iron and domestic scrap, into a rotary fragmentiser which pounds the charge into fist-sized pieces. Steel fragments are collected by strong electro-magnets, and the dust, paper, and plastic is sucked away by a powerful draught. The remaining combination of non-ferrous and non-metallic residues, containing the aluminium, is sent to a Heavy-media plant for further separation.

All the different metals are separated from one-another, and from the residues, by a series of processes. Flotation, sieving, and eddy-current separation, are commonly used. The resulting aluminium, which is predominantly casting grade, must conform to the specification for fragmentiser aluminium scrap set out by the ISRI 2 (code word 'twitch'). See Table 1.

London Metal Exchange. 2 International Scrap Recycling Institute.


Table 1 Specification for fragmentiser aluminium scrap

Contaminant Maximum limits

Free zinc 3% Free magnesium 1% Free iron and stainless 1.5% Non-metallic 5% (of which less than 1% is rubber and plastics)

Table 2 Alloy composition fragmentisor aluminium scrap and LM24

Element Si Cu Mg Zn Fe Mn Cr Ni Ti

Scrap 7+1 2.7-t- .9 .3+.15 1.5_+.2 1.1+.2 0.3 0.1 0.1 0.04 LM24 7.5/9.5 3/4 0.1 2.9 1.0 0.5 1.3 of Sn, Ni and other elements

A typical mix of alloying elements contained in fragmentisor aluminium scrap (Table 2) is similar to the LME specification for the standard casting alloy LM24 [8].

That the scrap is similar to LM24 confirms the dominance of aluminium castings from cars. But the magnesium content is higher than the LM24, indicating also the presence of wrought alloy. Only a moderate amount of grade modification, probably by diluting with virgin alloy, is needed to align the composition of the scrap alloy with that of the LME standard A380, confirming that today's fragmentiser aluminium scrap is a readily available and usable raw material. The situation for motor cars in the future is not so clear, and has been discussed in several previous papers [9-14] .

3. A i u m i n i u m usage in motor cars

According to the Aluminium Federation [ 15], the amount of aluminium used in an average European car (including those of Japanese origin) has increased 3-fold over the last 25 years: from 25 kg in 1960, to 75 kg in 1990. About 90% of this aluminium is used for castings, mainly engine and transmission applications, and the remainder is wrought, used for minor fittings and trims. All of the wrought aluminium is produced from primary metal smelted directly from bauxite. But about 65% of the cast aluminium is estimated to be secondary metal recycled from old scrap.

3.1. Changes to the materials used in cars

Two of the principal changes in technology adopted for the new generation of cars are a change from steel to aluminium for body structures, and from steel to aluminium for body panels [ 16-21 ]. Fig. 2 shows how the materials composition of today's car might compare to a typical aluminium car.

Some of the steel used in today' s car is replaced by aluminium and a composite, probably plastic. But the total amount of steel is still about half the weight of the car because of its continuing use for suspension, power train, and other items.

G. Hoyle /Resources, Conservation and Recycling 15 (1995) 181-191 185

100

75

%of Vehicle

50

25

Plastic/Foam

Fezzo~

Pl,utic/Foam

Composite

A~umL,~m

Fex, roa~

Fig. 2. Car compositions (various sources).

__------- ELutomer - - GL~

--------- No.-Fen, o~

An increased quantity of aluminium opens up new possibilities for recycling, but equally significant is the change in the ratio of wrought to cast grades of aluminium. Currently, aluminium applications in cars use about 10% wrought, and 90% cast, but when aluminium is substituted for steel panels and body frames, the ratio is likely to change to about 75% wrought, and 25% cast. This large quantity of wrought alloy is, in theory, available for recycling back in to wrought alloy, but first there are several barriers to overcome.

4. Barriers to recycling wrought scrap into wrought alloy

The current inability to adequately segregate differing grades of aluminium, is the fore- most factor impeding the recycling of wrought old scrap back into wrought ingot. Poor segregation results in scrap being contaminated, and a subsequent reduction in its value. Factors affecting the segregation of aluminium scrap from future cars are these:

4.1. Identification o f scrap

To sell the segregated aluminium scrap for a high price its series or grade must be known. Cast and wrought scrap is fairly easy to tell apart visually, and some heavy-media processes can separate them, but spotting the difference between one wrought grade and another is virtually impossible by inspection alone. It can only be achieved by fore-knowledge of the product or by sophisticated analysis.


IO0

scrap value

%LME 50

1

2 3

1 - F r a g m e n t i s e r Product 2 - Hand d ismant l ing cast /wrought 3 - Hand d ismant l ing , sort into g rades

s6 t60 segregation ¢o~rt

%LME Fig. 3. Segregation costs versus value as a percentage of LME price.

4.2. Segregation techniques

The principal method in use today of segregating scrap is fragmentising followed by heavy-media processing. This cost effective process works well provided that the desired end product is a homogenised mixture of many grades. It is, however, unable to discriminate individual series' or grades. Presently the only commercial alternative is hand dismantling and sorting. Fig. 3 shows how segregation costs and the value of the recovered product are related.

Clearly the most cost effective segregation technology is fragmentising. Despite being a mixture, fragmentiser aluminium scrap is of a known and guaranteed quality so it commands a high premium. Intuitively, cast and wrought alloy segregated by hand should have a higher value, but in reality it does not because it is expensive, and the product quality is hard to control.

4.3. Contamination from self-piercing rivets

The use of self-piercing rivets combined with adhesive bonding is a compelling choice for joining aluminium body structures and panels because it does not suffer the variable quality and expense of spot welded aluminium. But contamination of aluminium by steel from self-piercing rivets is an unattractive risk. Self-piercing rivets weigh 20 kg per 1000, so for a car body weighing 450 kg and using 500 rivets they could account for 2.2% of its weight. The tolerable limit for Iron in aluminium is low, about 0.5% for cast and 0.2--0.3% for wrought alloys. Not all the rivets will find their way into the aluminium smelting furnace because riveted extrusions should release the rivets in the fragmentiser in much the same way as cast aluminium fractures and releases steel fastenings. An alternative scenario, however, is that of wrought aluminium, being more ductile than cast alnminium, tending to fold up and trap the rivets, necessitating a costly second pass through a fragmentiser.

4.4. Non-metallic contamination

Manual dismantling and segregation of aluminium scrap does not remove paint, glue, grease, and mastic. These contaminants burn off in the furnace but in doing so create fumes


that increase the loading on the gas cleaning system. They also cause detrimental oxide products to form in the melt which have to be removed using salts. Some remelt companies surcharge for excessively contaminated scrap to cover the cost of purchase and disposal of purifying salts.

4.5. Design for recycling

The compatibility of the scrap depends on which grades are chosen for construction. A car made from a single grade of alloy is unlikely to be achieved, but careful design might limit the number of grades or ensure that only compatible grades are situated together. Compatible grades are only of use if the recycling channel can make good use of their inclusion. Much of the work done by car companies on single-alloys assumes closed-loop recycling and a workable method of segregation.

4.6. Obsolete grades

Those grades of aluminium which are only experimental today will probably be replaced by new grades as the industry converges on a standard composition. For example: 2000 series (copper based) grades are rarely fitted to today's technology demonstration cars. In 20 years time the alloys arising from scrap might well be incompatible with the standard alloys of the day, and therefore have reduced value.

4. 7. Remelting technology

Currently, the majority of scrap is remelted in rotating furnaces. The scrap melts down under the protection of a layer of salts to prevent excessive oxidisation. Despite this, a proportion of the charge is lost and must be replaced with costly virgin metal or fortified with alloying constituents. In the future new and innovative remelting furnaces based on reverberatory, plasma, and induction [ 22,23 ], principles of operation will accept scrap with a wider ranging composition than now and will suffer fewer losses.

5. Solutions to recycling wrought aluminium alloy

There are many possible solutions to the problem of segregation wrought aluminium. Chief among these are: do not segregate at all; make segregation unnecessary by improving the compatibility of the scrap; devise an identification system; or implement a motor-car- only recycling path to recycle aluminium within a closed-loop.

5.1. No segregation

Fragmentised aluminium scrap is a highly valued material. When melted and recast, it has a similar composition to the A380 alloy. But this fortunate coincidence may not continue if aluminium cars become commonplace. Arisings of old scrap from these new cars will not have a similar composition to A380 alloy because of the increased use of wrought

188 G. Hoyle / Resources, Conservation and Recycling 15 (1995) 181-191

aluminium in their construction. The implications are that segregation of cast and wrought grades will be essential to maintain a supply of secondary metal close to the A380 specification, or else the cost advantage of secondary aluminium may erode because alloying elements, refining agents, and virgin metal, will be required to bring the composition back to A380 standard.

5.2. Better compatibility of scrap arisings

In theory, using similar or compatible grades for all applications in car manufacture will reduce contamination of one grade by another when the car is scrapped. There are three approaches to achieving compatibility. The first is the introduction of a single all-purpose 'recycling alloy' that mirrors the average composition of the wrought scrap resulting from car structures. No such alloy has been developed that satisfies all the diverse requirements of an aluminium car. The second approach is to broaden the specifications of alloys to accommodate further impurities. Understandably, this proposal has not been taken up with enthusiasm. The third method is standardisation of grades used by all manufacturers. Whilst this is likely to happen anyway due to natural convergence on the best material for a given application, standardisation would be impractical to enforce and might be construed as stifling the freedom to innovate.

5.3. Improved methods of identification

Manufactures have adopted a marking system to aid the identification of plastics, and a similar system could be applied to aluminium. Manufacturers have also published lists of recyclable materials in 'recycling manuals'. Aluminium could be included in these as well.

Direct identification is another option. One of the more promising research areas is laser identification. This device recognises different grades of aluminium as the bits pass by the sensor head at high speed. Such a commercial product would segregate fragmentiser aluminium scrap into several categories.

5.4. Motor-car-only (closed-loop) recycling

This is an attractive idea. It would enable the industry to use general purpose alloys, build their cars out of compatible grades, or use whatever materials they liked, knowing that at the end of the car's life, a high-value scrap would be available. Sale of this scrap or substitution for new metal could then offset the high initial cost of aluminium. However, several factors affect the viability of such a scheme:

Competition for cars. Any recycling path for high-value scrap would have to compete for cars with established metal merchants. A car-only recycling centre may well not be able to pay enough to owners to attract a supply of cars, and remain viable. The minimum charge would be the scrap value, which for an aluminium car of the type proposed in this paper, would be about £250 at today's prices.

Value of the wrought scrap. Presently, hardly any wrought old scrap is bought or sold. If it were available in large quantities secondary smelters and primary smelters would both have good reasons to buy it. But currently there are is no firm guide as to the price that

G. Hoyle / Resources, Conservation and Recycling 15 (1995) 181-191

Table 3 Summary of recovery and dismantling costs

189

Item Destination Value (£)

Cost of car (scrap value) 250 Direct dismantling cost £20/h 50 Non-metallic waste disposal 10 Total costs 310

might be paid for it, or even if it would command a premium over existing fragmentiser scrap; although a figure of £100 has been suggested.

Uncertain savings. The cost benefits of using scrap could be passed on to the manufacturer directly or indirectly. Savings will pass directly to the buyer of semi-manufactured products if the price of secondary ingot or billet is less than virgin price at that time. Alternatively a smelter might do an exchange scheme, passing the saving on indirectly. A typical exchange of the type practised nowadays, is 3 of a ton of new metal for 1 ton of scrap. Currently the scrap industry works on a day-by-day basis buying low, storing until the market improves, and selling high. A glance around any scrap firm will show that it is not a minimal-inventory business!

Low margins. Currently the bulk of aluminium scrap is processed by the most cost effective means - a fragmentiser. However, this method is unable to segregate the low- value scrap from the high-value scrap desired. The alternative, hand dismantling, is practised only by scrap merchants and other fringe operators who have low overheads and can generate a margin. A professional organisation would be unlikely to generate any margin at all. This is shown by the approximate cost scenario for a lightweight car, set out in Table 3 and Table 4.

Given this scenario, four cars would be required to generate 1 tonne of high-value aluminium scrap. The cost of four cars, including the purchase, dismantling and disposal, is £1240. A substantial part of this is the cost of recovering cars; nearly two-thirds of the total, and indicating that control over car recovery is a key factor for success. This cost is likely to be high because of the scrap value of the aluminium, and it is likely to vary because of the volatility of aluminium prices. Some money might be recouped on the sale of residual scrap: engine, hulk, or plastics but not enough to cover costs.

An exchange agreement with a rate of about 3 on sheet material ( 3 tonne of new sheet in return for 1 tonne of scrap) might be viable, and assuming sheet costs are £2000 per tonne, the delivered cost of scrap would need to be less than £1500 per tonne to be viable.

Table 4 Summary of revenues

Item Destination Value (£)

Recovered high-value alloy smelter 150 Engine/power-train fragmentiser 25 Hulk for fragmentiser fragmentiser 15 Total revenue 190


Hand dismantling is capable of achieving £1240 per tonne. But this figure does not include capital costs, overheads, any return on investment. Clearly, any investment which gave little promise of a financial return and committed manufacturers to a costly recovery bill would be an unacceptable risk.

Extended life o f a luminium cars. A corrosion-resistant aluminium body will eliminate the principal reason for car s c r a p p a g e - structural failure. Such an aluminium car could last for over 25 years, according to Audi. But aluminium cars having such an extended life span would severely reduce the number of bodies available for recovery both in the short and long tenn. LandRovers have set a precedent; after 48 years in production more than 70% of those built are thought still to be in regular use. This implies that some form of life-span management, or car retirement plan, is needed to ensure a regular flow of scrap cars, but cars retired from service before their time still have a high resale value which will have to be accommodated, possibly within a novel ownership plan.

6. Concluding remarks

The risks and costs of systematic hand dismantling of wrought old scrap are such that it is unlikely to become established on a large scale. The same can be said for compulsory retirement of cars before their utility is exhausted.

Specific alloys will be recycled from old scrap when the technology has been developed to segregate them at low cost. Until then, aluminium scrap is l ikely to be recycled in the way it is now, that is, as remelted process scrap, or as fragmentised old scrap.

However, the changing balance of use in cars of cast alloys and wrought alloys might influence matters considerably. Provided that Iron contaminant is controlled, old scrap with a cast to wrought ratio of 1:3 will have an average composition very different from the 9:1 of today 's scrap. If it is close to that of a general-purpose alloy, requiring little modification to convert it into a recognisable high-value grade, wrought aluminium may be recycled by default. If on the other hand it is far from any standard grade, it will require substantial and costly refining.

References

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